Polymeric articulated beverage body door

ABSTRACT

An articulated door and door guiding track covers storage bays of a beverage body. An articulated door is formed by engaging a plurality of polymeric panel sections into a sequence such that each panel section can be positioned at varying angles with respect to an adjacent engaged panel section. The articulated door is guided between an open position and a closed position by a door guiding track comprised of a left channel facing a right channel across a door opening. The sequence of panel sections is slidably positioned in the door guiding track by having a left end of each panel section extending into the left channel and a right end of each panel section extending into the right channel.

This is a continuation of application Ser. No. 07/675,657, filed Mar. 27, 1991, now U.S. Pat. No. 5,165,746.

BACKGROUND OF THE INVENTION

The present invention relates to articulated doors for use in beverage bodies. More specifically, the present invention relates to an articulated door for use in a beverage body wherein the articulated door is formed from a sequence of engagable polymeric panel sections.

Beverage trailers and trucks employing beverage bodies have long been used to deliver beverages to various sorts of retailers. Articulated doors are typically used on both sides of a beverage body to permit access to individual storage bays where the beverages are stored. Under normal use, these doors are opened many times during the day as the driver delivers beverages to retailers along his route. While a general purpose delivery truck may use one roll-up door at the rear of the truck, a typical beverage body may use ten or more doors. Therefore, any disadvantage associated with a particular door design is multiplied many times when that design is employed in a beverage body.

Beverage bodies have typically employed articulated doors that are formed from a sequence of solid aluminum panel sections. These panel sections are formed with interlockable edges. Usually an aluminum panel section will have a first interlockable edge with an attached cylindrical structure and a second interlockable edge opposite the first edge with an attached, cylindrical structure having a radius larger than the radius of the cylindrical structure attached to the first edge. The smaller cylindrical structure of a panel section is placed within the larger cylindrical structure of an adjacent panel section thereby forming a joint that allows the two adjacent panel sections to be positioned at varying angles with respect to each other. The smaller cylindrical structure also includes a hollow center in which rollers are inserted. Therefore, every joint typically has a corresponding pair of rollers.

To guide an articulated aluminum door between an open position and a closed position, a door guiding track is required. A typical door guiding track is comprised of a pair of channels, with each channel having a pair of channel members facing each other across a gap in which the rollers are inserted. These channel members also may include track liners, often formed of stainless steel, to absorb vibrational energy and to reduce friction between the rollers and the channel members.

There are several problems that arise from using this type of articulated aluminum door in a beverage body. When doors of this type are new they typically work fine. However, as the beverage body is used, the door frame can be deformed by backing into loading docks and driving over rough roads and curbs. When the door frame is deformed, the door guiding track becomes out of square and the door will either jam or become very difficult to raise and lower.

As the beverage body is transported over roads with the articulated doors closed, the doors vibrate in their tracks. This vibrational energy is absorbed by the rollers and channel members as they vibrate against each other. This forms flat spots on the rollers and indentations in the channel members at the points where the rollers contact the channel members. As these indentations grow in size, the space surrounding the rollers increases, allowing the vibrations to increase in intensity and thereby increasing the rate at which the rollers and channel members deteriorate. These indentations also contribute to the door becoming more difficult to raise and lower.

As a door becomes more difficult to raise and lower, the rollers and channel members are lubricated. The lubrication eventually picks up dust and dirt which further accelerates the deterioration of the rollers and door guiding track. A delivery person will progressively exert more force to open and close the door as this deterioration cycle continues. Eventually a point will be reached when the delivery person will no longer be able to move the door. At this point the beverage body is brought back to the warehouse where typically a forklift is used to unjam the door, which usually destroys the door.

An articulated door and door guiding track that is constructed from self-lubricating materials and does not employ rollers would be resistent to deterioration and track alignment problems and would therefore be very desirable.

Because aluminum is not a resilient material, collisions with an articulated aluminum door usually result in a partial or complete destruction of the door. This can happen in a warehouse, where forklifts maneuver around and load beverage bodies, in an on-street accident, or from within the beverage body itself if the beverages contained therein should tip over. While the door can sometimes be repaired by replacing the impacted panel section, often adjacent panels will be deformed from the force transmitted through the interlocking edges.

When using beverage bodies in cold climates, the storage bays must be heated to prevent the beverages from freezing. Typically this is accomplished by circulating heated engine coolant from the tractor through the floor of the beverage body. Because aluminum is a highly thermo-conductive material, a layer of insulation must be added to the inner surface of an articulated aluminum door to retain the heat in the beverage body. This adds significant expense, complexity and weight to articulated aluminum doors used in beverage bodies.

Another problem associated with the use of beverage bodies in cold climates results from the salt and sand that is applied to road surfaces to melt ice and improve traction. The salt and sand work their way into the joints that connect adjacent panel sections, where they corrode and wear down the aluminum surfaces that form the joint. While the door can be steam cleaned, the joint has usually been damaged by the time this is done. Eventually the joint will lock up and the affected panel sections must be replaced.

Because of the weight of an articulated aluminum door, a counterbalance device is typically used to assist the delivery person in opening and closing the door. This device is usually located above the storage bay. The counterbalance adds weight and complexity to the beverage body and decreases the available space left to transport beverages.

An articulated door comprised of panel sections formed from a lightweight, high insulation, wear resistent, corrosion resistent and resilient material would be very desirable.

SUMMARY OF THE INVENTION

The present invention provides an articulated door and door guiding track for use in beverage bodies. To form an articulated door, a plurality of polymeric panel sections are engaged in a sequence of panel sections such that each panel section can be positioned at varying angles with respect to an adjacent engaged panel section.

The articulated door is guided between an open position and a closed position by a door guiding track. The door guiding track is comprised of a left channel facing a right channel across a door opening.

The sequence of panel sections are slidably positioned in the door guiding track with a left end of each panel section extending into the left channel and a right end of each panel section extending into the right channel.

The present invention provides an articulated door that is resilient, lightweight, wear resistent, corrosion resistent, self-lubricating and has a high insulation value. The present invention does not employ rollers to guide the door between the open position and the closed position and is relatively tolerant of door frame misalignment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a beverage body having articulated doors, with each articulated door supported by a door guiding track, in accordance with the present invention.

FIG. 2A is a transverse sectional view taken along line 2A--2A of FIG. 1 showing two articulated doors installed in a beverage body.

FIG. 2B is an enlarged sectional view of a section taken along line 2B--2B in FIG. 1 showing an articulated door of FIG. 2A.

FIG. 3A is a perspective view of a panel section, a plurality of which engaged in a sequence forms the articulated door of FIG. 1.

FIG. 3B is a transverse sectional view taken along line 3B--3B of FIG. 3A showing a panel section with a plurality of compartments which contain insulation.

FIG. 4A is a sectional view taken along line 4A--4A in FIG. 1 showing a pair of adjacent engaged panel sections, positioned in-line with each other, which form a segment of the articulated door of FIG. 1.

FIG. 4B shows the pair of adjacent engaged panel sections shown in FIG. 4A positioned at an angle with respect to each other.

FIG. 5 is a fragmentary perspective view of a panel section located at a bottom of the articulated door of FIG. 1, the panel section has a seal inserted into a bottom receptive edge and a slider plug (shown removed from a right end of the panel section).

FIGS. 6A and 6B are top cutaway views taken along lines 6A--6A and 6B--6B, respectively, of FIG. 1 showing panel sections inserted in door guiding tracks.

FIG. 7 is a sectional view taken along line 7--7 of FIG. 2B showing a slider plug inserted into a panel section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an articulated door and door guiding track for use in beverage bodies. The articulated door is formed from a plurality of polymeric panel sections and is guided between an open position and a closed position by a door guiding track.

FIG. 1 is a perspective view of beverage body 10. Beverage body 10 has floor 11, roof 13, generally vertical walls 9 intermediate the floor and the roof and a plurality of door openings in which articulated doors 12 are positioned. Beverage body 10 has an interior which is divided into individual beverage storage bays that are accessible by articulated doors 12. Articulated doors 12 are formed by engaging polymeric panel sections 14 into a sequence. A typical door of this type is 87 inches tall and 54 inches wide.

FIG. 2A is a transverse sectional view taken along line 2A--2A of FIG. 1 showing two articulated doors 12 installed in beverage body 10. Articulated doors 12 provide access to beverage storage bay 15 and are formed by engaging panel sections 14 into a sequence (this view does not show every panel section 14 required to form articulated door 12). Every alternate panel section 14 is provided with a pair of slider plugs 22. A bottom panel section 14, located adjacent to floor 11 of beverage body 10 when articulated door 12 is in the closed position, contains seal 23.

Articulated doors 12 are supported and guided by door guiding track 16. Each door guiding track 16 is comprised of a pair of channels 21, which face each other across the door opening. In this figure, only one channel 21 of each door guiding track 16 is visible. Each channel 21 includes channel members 18, which face each other across gap space 17, and curved segment 19, which is provided to guide articulated door 12 above beverage storage bay 15 and along roof 13 when door 12 is moved to the opened position. In one embodiment, articulated door 12 is connected to counterbalance 20 to assist the delivery person in moving articulated door 12 between the open position and the closed position. However, because of the light weight of articulated door 12, in another embodiment counterbalance 20 is not used.

FIG. 2B is a sectional view taken along line 2B--2B of FIG. 1. Every alternate panel section 14 is provided with a slider plug 22. Because slider plug 22 is wider than panel section 14, articulated door 12 is supported and guided by a contact between channel members 18 and slider plugs 22. The height of slider plug 22 is larger than the height of panel section 14. This allows slider plug 22 to partially cover the hinge between adjacent panel sections. This holds articulated door 12 together by preventing adjoining panel sections from sliding apart.

FIG. 3A is a perspective view of polymeric panel section 14. When a plurality of panel sections 14 are engaged in a sequence, they form articulated door 12 of FIG. 1. Panel section 14 has curved inner surface 24 and flat outer surface 26. Curved inner surface 24 has a preferred radius of 2.099 inches. This facilitates the movement of articulated door 12 through the curved section 19 of door guiding track 16 of FIG. 2A. Flat outer surface 26 is provided so that articulated door 12 can be easily painted with a beverage company's logo using a process such as silk-screening. Curved inner surface 24 and flat outer surface 26 are connected to each other by a plurality of parallel partitions 28. Plurality of parallel partitions 28 divides a space between flat outer surface 26 and curved inner surface 24 into a plurality of parallel compartments 30. This increases the strength and insulation properties of panel section 14 while decreasing the weight of the panel section.

An articulated door formed from a plurality of panel sections 14 will have an insulation value approximately twice that of an insulated aluminum door of the prior art. Therefore, for most applications, the articulated door of the present invention will not require any additional insulation. However, if a beverage body is to be used in extremely cold climates, or an articulated door is to be used in an application where a high insulation value is crucial, panel section 14 can be easily and inexpensively provided with insulation. FIG. 3B is a transverse sectional view taken along line 3B--3B of FIG. 3A. In an alternative embodiment shown in FIG. 3B, the plurality of parallel compartments 30 of panel section 14 are filled with urethane foam insulation 31. This greatly enhances the insulation value of panel section 14 without changing the external dimensions of the panel section or an articulated door constructed therefrom.

In FIG. 3A, panel section 14 has right end 32 and left end 34 (named with respect to viewing a panel section 14 in an articulated door 12 from an exterior of beverage body 10 of FIG. 1). Right end 32 and left end 34 expose the plurality of parallel compartments 30. Panel section 14 also includes top hook edge 36 and bottom receptive edge 38, which engage with adjoining panel sections 14 to form articulated door 12 of FIG. 1. Ideally, a distance between top hook edge 36 and bottom receptive edge 38, i.e., the height of panel section 14, is as large as possible. As this distance becomes larger, fewer panel sections 14 are required to form articulated door 12, thereby decreasing the cost of the door. However, as the height of the panel sections increases, so must the radius of curved section 19 of door guiding track 16 of FIG. 2A. Therefore, the preferred height of panel section 14 is 2.430 inches to facilitate a articulated door 12 formed from an acceptable number of panel sections 14 while maintaining an acceptable radius for curved section 19 of door guiding track 16.

Panel section 14 is formed by an extrusion process using a material that is a polymer blend of polyphenylene oxide and high impact polystyrene with triarylphosphate esters added to retard fire. Different variants of the polymer blend can be used based on the climate where the articulated door will be used. Compared to aluminum, the polymer blend used in the present invention has a high insulation value and is lightweight, resilient, self-lubricating, wear resistent and corrosion resistent. Parallel partitions 28, curved inner surface 24, flat outer surface 26, top hook edge 36, bottom receptive edge 38 and other extruded walls are formed with a thickness of 0.05 inches.

FIG. 4A is a sectional view taken along line 4A--4A of FIG. 1 showing a pair of adjacent engaged panel sections 14 that form a segment of the articulated door 12 of FIG. 1. The two panel sections 14 are shown positioned with respect to each other as they would be when the door is in the closed position. Top hook edge 36 is engaged with bottom receptive edge 38 to form hinge 40, with top hook edge 36 positioned generally within bottom receptive edge 38. Hinge 40 allows the pair of adjacent engaged panel sections 14 to be positioned at varying angles with respect to each other.

FIG. 4B is a view similar to FIG. 4A, with the adjacent panel sections 14 positioned at an angle with respect to each other. Two adjacent panel sections 14 would be positioned in such a way as they move through curved section 19 of door guiding track 16 of FIG. 2A.

FIG. 5 is a fragmentary perspective view of a bottom panel section 14 that is located at a bottom end of articulated door 12. When articulated door 12 is in the closed position, as shown in FIG. 1, bottom panel section 14 is located adjacent to floor 11 of beverage body 10. Bottom panel section 14 has seal 23 inserted in bottom receptive edge 38. Seal 23 seals a gap between floor 11 of beverage body 10 and the bottom end of articulated door 12 when door 12 is in the closed position.

Also shown in FIG. 5 (removed from right end 32 of panel section 14) is slider plug 22. Slider plug 22 is formed from a low density ultra-high molecular weight polyethylene plastic and is comprised of end plate 46 and plurality of fingers 48. Each finger 48 has a plurality of deflectable retention tabs 50 positioned perpendicularly to finger 48 and parallel with the end plate 46. Slider plug 22 also includes outer surface plate 52 which extends perpendicularly from end plate 46 and is parallel with the plurality of fingers 48.

The sequence of panel sections 14 that forms articulated door 12 alternates between a first panel section and a second panel section. A slider plug 22 is positioned on right end 32 and left end 34 (shown in FIG. 3) of every first panel section in the sequence. In other words, a pair of slider plugs 22 is provided for every alternate panel section 14 in the sequence of panel sections that forms articulated door 12. As shown in FIG. 7, which is a sectional view taken along line 7--7 of FIG. 2, slider plug 22 is attached to an end of panel section 14 by having each of the plurality of fingers 48 of slider plug 22 placed in a parallel compartment 30, with the plurality of deflectable retention tabs 50 of each finger 48 in contact with an interior surface of the corresponding, parallel compartment 30 and outer surface plate 52 (shown in FIG. 5) extending out over flat outer surface 26 of panel section 14.

End plate 46 is large enough to partially cover top hook edge 36 and bottom receptive edge 38. This holds the articulated door together by preventing two adjacent engaged panel sections from sliding apart from each other. In the case of the bottom panel section 14 shown in FIG. 5, end plate 46 also prevents seal 23 from sliding out of bottom receptive edge 38.

FIG. 6A is a fragmentary cutaway view showing panel section 14 and door guiding track 16 taken along line 6A--6A of FIG. 1. Door guiding track 16 includes a pair of channels 21, one of which is shown in this figure. Channel 21 includes channel members 18 facing each other across gap space 17. Panel section 14 has slider plug 22 inserted into left end 34. The distance between curved inner surface 24 and flat outer surface 26, i.e., the width of panel section 14, is preferably 0.515 inches, while the preferred width of slider plug 22 is 0.575 inches. Because slider plug 22 is wider than panel section 14, panel section 14 is not in direct contact with door guiding track 16.

In this embodiment, track liner 54 is positioned over a channel member 18 that faces curved inner surface 24 of panel section 14. Track liner 54 is formed from a high density ultra-high molecular weight polyethylene plastic. This produces a sliding, self-lubricating, plastic-on-plastic contact between slider plug 22 and track liner 54. This embodiment is used in door guiding tracks that have been converted to the present invention from door guiding tracks of the prior art.

FIG. 6B is a fragmentary cutaway view showing panel section 14 and door guiding track 16 taken along line 6B--6B of FIG. 1. Right end 32 is positioned in gap space 17 of channel 21. In this embodiment, a three-sided integrally formed track liner 56 is placed in channel 21. Track liner 56 is formed from a high density ultra-high molecular weight polyethylene plastic. This produces a sliding, self-lubricating, plastic-on-plastic contact between slider plug 22 and track liner 56. This embodiment is used in door guiding track of new construction.

The present invention improves the operation of articulated doors and door guiding tracks in beverage bodies by eliminating the rollers required in the prior art. The rollers are replaced by a sliding, self-lubricating, plastic-on-plastic contact that supports and guides the articulated door as it is moved between the open position and the closed position, thereby making the door less sensitive to door frame misalignment.

The articulated door of the present invention will last longer than articulated aluminum doors of the prior art. The plastic-on-plastic contact in the hinges that connect adjacent panel sections can outwear the aluminum-on-aluminum contact in the hinges of the prior art by a factor of approximately 6 to 1. Although both plastic and aluminum can be steam cleaned, any salt, sand, or dirt that gets into an aluminum hinge will take a toll in wear and corrosion before it can be removed. In contrast, when a plastic hinge is steam cleaned and the salt, sand and dirt are removed, the underlying plastic surfaces of the hinge are left largely unaffected because the plastic used in the present invention is highly corrosion resistent and wear resistent.

The articulated door of the present invention weighs less the one-half the weight of articulated aluminum doors of the prior art. This results in a weight reduction of more than 500 pounds in a typical beverage body. In addition, because of the door's light weight, the counterbalance used in articulated aluminum doors of the prior art may not be needed, further decreasing the cost and weight of the beverage body.

Compared to aluminum, which is highly thermoconductive, the plastic used to form the articulated door of the present invention has a very high insulation value. While an articulated aluminum door of the prior art will require a layer of insulation to be attached for use in cold climates, the articulated door of the present invention probably will not require additional insulation. However, if additional insulation is required, foam insulation can be placed inside the plurality of compartments of the panel sections to increase the insulation value of the door.

The articulated door of the present invention is resilient; articulated aluminum doors of the prior art are not. The door is much less likely to be damaged from impacts and collisions than are aluminum doors of the prior art. If the door is impacted, the panel sections probably will not break, but instead may pop out of the door guiding track and the hinges that connect the panel sections to adjacent panel sections. Most likely the panel sections will not be damaged and the door can be reassembled.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A beverage body for transporting beverages, the beverage body comprising:a floor; a roof; a plurality of generally vertical walls intermediate to the floor and the roof and forming an interior of the beverage body; a plurality of beverage storage bays located in the interior; and a plurality of articulated, manually operable, rollerless doors with each door providing access to one of the storage bays and manually movable between an open raised position, wherein the door is stored along the roof, and a closed lowered position, wherein each door is comprised of: a door opening in one of the generally vertical walls; a left channel comprised of a pair of left channel members with at least one of the left channel member having a plastic contact surface, the left channel having a generally vertical section positioned along a left side of the door opening for supporting a left side of the door in the closed lowered position, a generally horizontal section positioned along the roof for supporting the left side of the door when the door is stored in the open raised position, and a curved section that connects the vertical section to the horizontal section; a right channel comprised of a pair of right channel members with at least one of the right channel members having a plastic contact surface, the right channel having a generally vertical section positioned along a right side of the door opening for supporting a right side of the door in the closed lowered position, a generally horizontal section positioned along the roof for supporting the right side of the door when the door is stored in the open raised position, and a curved section that connects the vertical section to the horizontal section; and a plurality of polymeric panel sections connected together such that a hinge is formed between adjacent panel sections, the hinge allowing the adjacent panel sections to be positioned at varying angles with respect to each other, wherein each panel section includes:a left end which extends into the left channel to provide a non-rotatable, sliding and self-lubricating, rollerless engagement with the plastic contact surface of the left channel; and a right end which extends into the right channel to provide a non-rotatable, sliding and self-lubricating, rollerless engagement with the plastic contact surface of the right channel.
 2. The beverage body of claim 1 wherein each panel section comprises:a flat outer surface; a curved inner surface; a plurality of partitions connecting the outer surface to the inner surface and separating a space between the outer surface and the inner surface into a plurality of compartments; a bottom receptive edge positioned adjacent to the outer surface and the inner surface and connecting the left end to the right end; and a top hook edge positioned opposite the bottom receptive edge, adjacent to the outer surface and the inner surface and connecting the left end to the right end, for engaging the bottom receptive edge of a like panel section by being generally positioned within the bottom receptive edge of the like panel section to form the hinge between the adjacent panel sections.
 3. The beverage body of claim 2 wherein for each panel section the plurality of partitions are parallel with each other and are parallel with the top hook edge and the bottom receptive edge.
 4. The beverage body of claim 3 wherein for each panel section each end is open and exposes the plurality of partitions and the plurality of compartments.
 5. The beverage body of claim 4 and further comprising a plurality of pairs of polymeric slider plugs wherein each pair of slider plugs is attached to one of the plurality of panel sections, with a first slider plug of the pair attached to the left end of the one panel section, and a second slider plug of the pair attached to the right end of the one panel section.
 6. The beverage body of claim 5 wherein each slider plug comprises:an end plate; a plurality of fingers extending perpendicularly from the end plate; and a plurality of deflectable retention tabs attached perpendicularly to each finger; whereinthe slider plug is attached to one of the left or right ends of the one panel section of the plurality of panel sections by having each finger placed in one compartment of the plurality of compartments with at least one retention tab of the plurality of retention tabs in contact with an interior surface of the one compartment, wherein the end plate of the slider plug extends over the outer surface of the one panel section, and the end plate extends partially over at least one hinge formed with at least one adjacent panel section.
 7. The beverage body of claim 5 wherein the plurality of panel sections are connected in a sequence which alternates between a first panel section and a second panel section, and one pair of the plurality of slider plugs is provided for every first panel section in the sequence.
 8. The beverage body of claim 5 wherein each polymeric slider plug is formed from an ultra-high molecular weight polyethylene plastic.
 9. The beverage body of claim 2 and further including a seal wherein a part of the seal is positioned within and retained by the bottom receptive edge of a last panel section of the plurality of panel sections that does not have the bottom receptive edge thereof engaged with another panel section, and a remainder of the seal extends out from the bottom receptive edge of the last panel section.
 10. The beverage body of claim 2 wherein the flat outer surface of at least one panel section of at least one door is painted by a process of silk-screening.
 11. The beverage body of claim 1 wherein each plastic surface is formed from a high density ultra-high molecular weight polyethylene plastic.
 12. The beverage body of claim 1 wherein each polymeric panel section is formed from a polymer blend which includes polyphenylene oxide.
 13. The beverage body of claim 12 wherein the polymer blend further includes triarylphosphate esters to retard fire and high impact polystyrene.
 14. The beverage body of claim 1 wherein at least one articulated door is about 87 inches tall and 54 inches wide.
 15. An articulated, manually operable, rollerless door about 87 inches tall and about 54 inches wide, for use in a beverage body having a floor, a roof, a plurality of generally vertical walls intermediate to the floor and the roof, and a plurality of beverage storage bays located in an interior of the beverage body, the door being manually movable between a closed lowered position and an open raised position, wherein the door is stored along the roof, the door comprising:a door opening in one of the walls; a left channel comprised of a pair of left channel members with at least one of the left channel members having a plastic contact surface, the left channel having a generally vertical section positioned along a left side of the door opening for supporting a left side of the door in the closed lowered position, a generally horizontal section positioned along the roof for supporting the left side of the door when the door is stored in the open raised position, and a curved section that connects the vertical section to the horizontal section; a right channel comprised of a pair of right channel members with at least one of the right channel members having a plastic contact surface, the right channel having a generally vertical section positioned along a right side of the door opening for supporting a right side of the door in the closed lowered position, a generally horizontal section positioned along the roof for supporting the right side of the door when the door is stored in the open raised position, and a curved section that connects the vertical section to the horizontal section; and a plurality of polymeric panel sections connected together such that a hinge is formed between adjacent panel sections, the hinge allowing the adjacent panel sections to be positioned at varying angels with respect to each other, wherein each panel section is about 2.4 inches tall and about 0.5 inches thick, each panel section including:a left end which extends into the left channel to provide a non-rotatable, sliding and self-lubricating, rollerless engagement with the plastic contact surface of the left channel; a right end which extends into the right channel to provide a non-rotatable, sliding and self-lubricating, rollerless engagement with the plastic contact surface of the right channel; a flat outer surface; a curved inner surface; a plurality of partitions connecting the outer surface to the inner surface and separating a space between the outer surface and the inner surface into a plurality of compartments; a bottom receptive edge positioned adjacent to the outer surface and the inner surface and connecting the left end to the right end; and a top hook edge positioned opposite the bottom receptive edge, adjacent to the outer surface and the inner surface and connecting the left end to the right end, for engaging the bottom receptive edge of a like panel section by being generally positioned within the bottom receptive edge of the like panel section to form the hinge between the adjacent panel sections. 